In a water-cooled outboard engine, it is known to have cooling water sucked by means of a water pump provided within a gear case, to circulate it through a cylinder jacket, and to then discharge it from the system. The circulation of the cooling water stops if the suction inlet therefor becomes clogged, or if the water pump breaks down, leading to overheating of the engine and thereby causing damage to the cylinder or a piston.
Further, if a propeller with a smaller pitch than the standard value is used, or one with the standard pitch but a small load, the engine speed increases to an undesirable level, thereby reducing the life of the engine to a remarkable extent.
Recently, a separate oiling type of outboard engine has been widely used. In such an outboard engine, when the level of oil drops to or below a prescribed level, or when an oil filter becomes clogged, the operator must be warned in some way of the shortage of oil or of the clogging of the filter.
An alarm device for outboard engines is required from the above-described viewpoints.
A known alarm device for outboard engines is of a type which includes a control system for controlling the ignition so as to maintain the engine speed below a fixed value when the engine speed becomes too high because of the use of a propeller with a smaller pitch than the standard value or owing to the generation of cavitation during running, and which at the same time generates an alarm to the operator by an alarming means such as a buzzer when this control system which prevents excessive engine speed is operated, when the circulation of cooling water stops due to an abnormality generated in the cooling system of the engine, when the oil level drops to an alarming level in a separate oiling engine, or when the oil does not flow due to clogging of an oil filter.
However, with such an alarm device, the audio volume of the alarms must be very high, in particular during high speed running. Otherwise, it might not be heard by the operator, because the engine sound and wind noise are relatively high. On the other hand, if the volume is adjusted so that the alarm can be heard at high speed running, it becomes too high during idling (trawling) or medium speed running.
In view of the above-described problem of known systems, an object of the present invention is to provide an audio alarm outputting device for an outboard engine which is capable of automatically changing the audio volume of the alarm in accordance with the speed of the outboard engine so as to enable an operator to easily detect and recognize alarms associated with abnormalities of the outboard engine, regardless of the speed thereof.